<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Set 实践</title>
</head>
<body>
    <script>
        let arr = [1, 2, 3, 4, 5, 4, 3, 2, 1];
        //1.数组去重
        //let result = [... new Set(arr)]
        //console.log(reult);
        //2.交集
        let arr2 = [4, 5, 6, 5, 6];
        let result = [... new Set(arr)].filter(item => {
            let s2 = new Set(arr2); // 4 5 6
            if(s2.has(item)) {
                return true;
            } else {
                return false;
            }
        });

        //简化写法
        let results = [... new Set(arr)].filter(item => new Set(arr2).has(item));
        console.log(results);
        //3.并集
        let union = [... new Set([...arr, ...arr2])];
        console.log(union);

        //4.差集
        let resultss = [... new Set(arr)].filter(item => !(new Set(arr2).has(item)));
        console.log(resultss);
    </script>
</body>
</html>